The invention relates to an apparatus and method for manufacturing a molded glass stem, and more particularly to an apparatus and method for manufacturing a stem having a plurality of lead-in conductors of various internal lengths.
During the process of stem manufacturing, the individual lead-in conductors or leads must be supported at the top and the bottom during a press operation to insure proper positioning of the sealing portion of the leads within the glass fillets of the stem. Where the lead-in conductors comprise a three piece lead with an external and an internal section and a central Dumet section, it is important that the Dumet section be bonded securely within the glass fillets of the stem.
In the prior art it was conventional that the lead-in conductors were made having the same internal length. In order to attach the electron gun to the leads it was necessary to trim the internal portions of at least some of the leads to obtain the desired length. This trimming operation frequently caused chips in the glass fillets surrounding the leads and in some instances caused vacuum leaks through the stems and/or the generation of glass particles within the finished tube. Such a condition could result in failure of the tube or in rejection of the final tube for particles which adhere to the shadow mask and block the apertures thereof producing spots on the output screen of the tube.
In order to improve tube quality and to reduce the manufacturing costs involved with lead trimming and inspection of the stems, it is desirable to manufacture a stem having internal leads of the required lengths. Such a lead structure would facilitate attaching the internal components thereto without further trimming or inspection operations that are now required under conventional procedures.
Prior art stem molds include an upper and a lower section and necessitate the application of sufficient weight to the lead-in conductors to immobilize the lead-in conductors during the stem manufacturing operation. The high temperatures involved in melting the glass of the stem during stem manufacturing make it advisable for the lead-weights, which rest upon the internal portions of the lead-in conductors, to be sufficiently far away from the heat to prevent damage to the lead weights. Prior attempts to make stems having lead-in conductors of various internal lengths have required the frequent replacement of lead-weights due to thermal distortion or deterioration thereof. Additionally, it is difficult to manufacture stems of different internal lead lengths using conventional stem-making equipment, since any changes in the internal lengths of the lead-in conductors require corresponding changes in the lengths of the lead-weights.
It is therefore desirable that an apparatus and method be provided which will allow a modification of conventional stem molds, using lead-weights of uniform length, to provide stems having lead-in conductors of different internal lengths.